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NMO AND CLASS ALSO WE HAVE SOMETHING CALLED DTM (Dual Transfer Mode)Similar to GSM, the data transferred over the GPRS network can be both user data and

Signaling data. Signaling data is exchanged for example during the followingprocedures:-

The network pages the mobile station to inform it of incoming packets.

The network pages the mobile station to inform it of incoming packets.

The mobile station accesses the network to request resources (PDTCHs) to sendpackets.

The mobile station accesses the network to request resources (PDTCHs) to sendpackets.

Modification of resources assigned to a subscriber.

Modification of resources assigned to a subscriber.

Acknowledgment of correct reception of user data packets.

This can be done in a number of ways:-

In GPRS, network operation mode I (NOM I) signaling for packet- and circuit-switched

data is done either via the GSM paging channel (PCH) or the GPRS packet pagingchannel

(PPCH) if it is available. To make sure incoming voice calls are not missed by class Bmobile

stations during an active data transfer, an interface between the circuit-switched part(MSC)

and the packet-switched part (serving GPRS support nodeSGSN) of the network isused.

This interface is called the Gs interface. Paging for incoming circuit-switched calls willbe

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NMO AND CLASS ALSO WE HAVE SOMETHING CALLED DTM (Dual Transfer Mode)forwarded to the packet-switched part and then sent to the mobile as shown in Figure2.10.

If a packet data transfer is in progress when a paging needs to be sent, the mobile willbe

informed via the packet associated control channel (PACCH) to which the circuit-switched

GSM part of the network does not have access. Otherwise, the paging is done via thePCH

or the PPCH. The Gs interface can also be used for combined GSM/GPRS attachprocedures

and location updates. NOM I is the only mode in which the Gs interface is available and

thus the only mode in which the mobile is capable of receiving the paging during anongoing

data transfer. As the Gs interface is optional, it is not widely used in networks today.

However, most network vendors have implemented this interface and a number ofoperators

have begun using it to enhance their networks behavior for subscribers during GPRS

sessions.

The GPRS NOM II is the simplest of the three network modes and therefore commonly

used today. There is no signaling connection between the circuit-switched andpacketswitched

part of the network and therefore the PPCH is not present. For more on this see the

next section. This has the disadvantage that the mobile will not see incoming circuit-switched

calls during packet-switched data transmission as described before.

And finally there is NOM III. In this mode the Gs interface is not available and thus

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NMO AND CLASS ALSO WE HAVE SOMETHING CALLED DTM (Dual Transfer Mode)the circuit-switched paging has to be done over the PCH. In this mode, the GPRScommon

control channel with its subchannels PPCH, PRACH, and PAGCH is available and the

packet-switched side performs its signaling via its own channels. This mode might be

preferable to NOM II in some situations as it reduces the traffic load on the PCH, which

is used heavily in operational networks for paging messages, random access requestsand

assignment requests for circuit-switched services.

To inform users which of these GPRS network modes is used, GPRS uses the GSM

broadcast common control channel (BCCH).

Acknowledgment of correct reception of user data packets.

This can be done in a number of ways:-

In GPRS, network operation mode I (NOM I) signaling for packet- and circuit-switched

data is done either via the GSM paging channel (PCH) or the GPRS packet pagingchannel

(PPCH) if it is available. To make sure incoming voice calls are not missed by class Bmobile

stations during an active data transfer, an interface between the circuit-switched part(MSC)

and the packet-switched part (serving GPRS support nodeSGSN) of the network isused.

This interface is called the Gs interface. Paging for incoming circuit-switched calls willbe

forwarded to the packet-switched part and then sent to the mobile as shown in Figure2.10.

If a packet data transfer is in progress when a paging needs to be sent, the mobile willbe

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NMO AND CLASS ALSO WE HAVE SOMETHING CALLED DTM (Dual Transfer Mode)informed via the packet associated control channel (PACCH) to which the circuit-switched

GSM part of the network does not have access. Otherwise, the paging is done via thePCH

or the PPCH. The Gs interface can also be used for combined GSM/GPRS attachprocedures

and location updates. NOM I is the only mode in which the Gs interface is available and

thus the only mode in which the mobile is capable of receiving the paging during anongoing

data transfer. As the Gs interface is optional, it is not widely used in networks today.

However, most network vendors have implemented this interface and a number ofoperators

have begun using it to enhance their networks behavior for subscribers during GPRS

sessions.

The GPRS NOM II is the simplest of the three network modes and therefore commonly

used today. There is no signaling connection between the circuit-switched andpacketswitched

part of the network and therefore the PPCH is not present. For more on this see the

next section. This has the disadvantage that the mobile will not see incoming circuit-switched

calls during packet-switched data transmission as described before.

And finally there is NOM III. In this mode the Gs interface is not available and thus

the circuit-switched paging has to be done over the PCH. In this mode, the GPRS

common

control channel with its subchannels PPCH, PRACH, and PAGCH is available and the

packet-switched side performs its signaling via its own channels. This mode might be

preferable to NOM II in some situations as it reduces the traffic load on the PCH, which

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NMO AND CLASS ALSO WE HAVE SOMETHING CALLED DTM (Dual Transfer Mode)is used heavily in operational networks for paging messages, random access requestsand

assignment requests for circuit-switched services.

To inform users which of these GPRS network modes is used, GPRS uses the GSM

broadcast common control channel (BCCH).

Network operation mode and phone classes

The Network Operation Mode, or NOM, is responsible for the capabilities of a GPRSnetwork, while the class indicates the mobile phone capabilities. On NOM 1 networks,

mobile phones with the right capabilities can have simultaneous circuit- and packet-switched connections. On NOM 2 networks, mobile phones can remain attached to theGPRS networks when in a voice call but they can't transmit data at the same time. OnNOM 3 networks, mobile phones can either establish a packet-switched dataconnection or a circuit-switched voice one but they need to disconnect from one toestablish another.Class A phones can make full use of NOM 1 networks: they can use circuit-switched voice and GPRS data services at the same time. Class B phones can

register circuit-switched voice and packet-switched data services at thesame time but may only use one at a time. Should the user receive a call

while on the internet, they can take the call and GPRS service will besuspended, resuming once the voice call is ended. Resuming GPRS service is

much faster than re-establishing a data call. Class C phones can onlyregister for packet-switched data or for circuit-switched voice services; if the

user chooses GPRS, then they will be totally unavailable for GSM calls andreciprocally.

End-users will initially have access to Class B mobile phones, which are ableto make and receive calls while simultaneously being registered with GPRS

services - GPRS services will automatically be suspended and resumed at the

end of the call. Class B phones only support one active service at a time -GSM (voice, fax or data) or GPRS (data) - though both services can be

registered with the network and the phone can switch automatically backand forth. However, should the user roam to a network area that is NOM III,

their Class B phone will effectively be working as a Class C phone.

New applications designed to run in an online environment will be developed

to take advantage of GPRS and 3G networks. The user may well experience

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NMO AND CLASS ALSO WE HAVE SOMETHING CALLED DTM (Dual Transfer Mode)

a 'blurring' of applications whereby they won't need to switch task nearly at

all.